Hirotaka Geka

Properties and applications of Sn-doped single crystal thin film magneto-resistance elements

Using Sn-doped single crystal InSb thin films of 1.0-/spl mu/m thickness grown on GaAs substrates by molecular beam epitaxy, new magneto-resistance elements with very small temperature dependence were developed. Using these magneto-resistance elements, the contactless detection of the rotation speed of rotating gear teeth over a wide range of rotation speeds was studied. The output voltage from the magneto-resistance element was independent of the rotation speed of the gear, and exhibited good temperature stability and very small sine wave sine wave distortion, which allowed fine detection of the angular velocity of the rotations.

Real-time observation of rotational twin formation during molecular-beam epitaxial growth of GaAs on Si (111) by x-ray diffraction

The formation and evolution of rotational twin (TW) domains introduced by a stacking fault during molecular-beam epitaxial growth of GaAs on Si (111) substrates were studied by in situ x-ray diffraction. To modify the volume ratio of TW to total GaAs domains, GaAs was deposited under high and low group V/group III (V/III) flux ratios. For low V/III, there was less nucleation of TW than normal growth (NG) domains, although the NG and TW growth rates were similar. For high V/III, the NG and TW growth rates varied until a few GaAs monolayers were deposited; the mean TW domain size was smaller for all film thicknesses.

Interfacial trap states and improvement of low-temperature mobility by doping in InSb/AlInSb quantum wells

The effect of doping on InSb/Al0.1In0.9Sb quantum wells (QWs) was investigated, and it was found that doping improves the electron mobility at low temperatures and leads to a weaker dependence of the resistivity with temperature. The dependence of the carrier density on the well width revealed trap states at the interfaces of the QW whose sheet density per interface was estimated to be about 4 × 1010 cm−2. The low mobility of undoped InSb QWs, in particular, at low temperature seems to have been caused by positively ionized impurity scattering at the interfacial trap states. Doping compensates for the trap states and enhances mobility by suppressing ionized impurity scattering. Thus, intentional doping is necessary for developing high-mobility InSb QW devices. The origin of the trap states is qualitatively discussed.

Transport properties and observation of quantum Hall effects of InAs 0.1 Sb 0.9 thin layers sandwiched between Al 0.1 In 0.9 Sb layers

InAs0.1Sb0.9 active layers sandwiched between Al0.1In0.9Sb insulating buffer layers were grown on GaAs (100) substrates by molecular beam epitaxy. The basic transport properties at room temperature and quantum Hall effects at low temperature of the InAs0.1Sb0.9 were studied as a function of InAs0.1Sb0.9 thickness. The electron mobility of the InAs0.1Sb0.9 active layers had a very high value and very small thickness dependence at less than 500nm. The quantum Hall effects of the InAs0.1Sb0.9 were observed at thicknesses 15, 20, 30, 50, 70, and 100nm. The observation of the quantum Hall effect at thickness more than 50nm strongly suggests the existence of two-dimensional electron gas in the InAs0.1Sb0.9 layer sandwiched between Al0.1In0.9Sb layers.

Negative and Positive Magnetoresistance in Variable-Range Hopping Regime of Undoped AlxIn1−xSb/InSb Quantum Wells

Low-temperature magnetoresistance (MR) in the variable-range hopping (VRH) regime of undoped AlxIn1−xSb/InSb quantum wells was studied. The low-T resistance shows that the two dimensional (2D) Mott VRH crossovers to Efros-Shklovskii (ES) VRH due to the Coulomb interaction with lowering T. The anisotropic negative MR in weak magnetic fields was explained by the quantum interference in the VRH. The in-plane positive MR in higher fields found in ES VRH regime was attributed to the spin-Zeeman effect that suppresses the hops between singly occupied states in the presence of intra-state correlation. As for the orbital MR subtracted from perpendicular MR, in deeply insulating regime the negative MR saturates above a characteristic field followed by an exponential increase of the positive MR in agreement with the quantum interference and the subsequent shrinkage of wave functions with increasing field, while in barely insulating regime of the 2D metal-insulator (MI) transition a large negative MR inexplicable survives even in the extremely high magnetic-fields.

Transport Properties of InAs0.1Sb0.9 Thin Films Sandwiched by Al0.1In0.9Sb Layers Grown on GaAs(100) Substrates by Molecular Beam Epitaxy

Electron mobilities of InSb, InSb/AlInSb and InAsSb/AlInSb grown on GaAs(100) were compared as a function of layer thickness and temperature. InAs0.1Sb0.9 thin active layers sandwiched by Al0.1In0.9Sb layers showed the smallest thickness dependence and very large electron mobility at less than 500nm thickness. Basic transport properties and Sn doping effects of the InAs0.1Sb0.9 were studied.

NDIR gas sensing using high performance AlInSb mid-infrared LEDs as light source

In this paper, we report the performance of room temperature operated mid-infrared light emitting diode (LED) with an InSb buffer layer and AlInSb active/barrier layers, which showed to be suitable for non-dispersive infrared (NDIR) gas sensing. Characterization of the LED was performed and we found that good carrier confinement and crystalline quality was responsible for its high performance. High efficiency light extraction was obtained by adopting backside emission architecture together with surface roughening treatment and TiO2 anti-reflection coating. The fabricated AlInSb LED showed 75% higher power conversion efficiency when compared with a commercially available device. The developed LED, together with a commercially available infrared (IR) detector equipped with band-pass optical filter (AK9710, manufactured by Asahi Kasei Microdevices) were coupled into a mirror system forming a light path length of 80 mm, which was tested for CO2 gas sensing. For a non-absorbing environment, sensor output of 8 nA was obtained by driving the LED with peak current of 100 mA and, by exposing the system at CO2 concentration of 1000 ppm signal reduction due to absorbance around 12% was obtained.

Relationship between transport properties and band diagrams in InAsxSb1−x/Al0.1In0.9Sb quantum wells

The resistivity of InAs0.1Sb0.9/Al0.1In0.9Sb quantum wells (QWs) is much lower than that of InSb/Al0.1In0.9Sb QWs, staying low resistivity even at low temperature. Fundamental difference in low temperature transport properties between InSb/Al0.1In0.9Sb and InAs0.1Sb0.9/Al0.1In0.9Sb QWs was revealed, based on the band diagram calculations of these QWs. Band diagrams of InAsxSb1−x/Al0.1In0.9Sb QWs showed that the energy band of the InAsxSb1−x layer moves downward with increasing As content x. The QW is type I at x equal to 0, becomes type II at x equal to 0.1. The Fermi level (EF) of the InSb QWs lies in the band gap and below apart from the bottom of the conduction band, while EF of the InAs0.1Sb0.9 QWs is above the bottom of the conduction band of the well. The calculated sheet carrier densities are in good agreement with the experimental results. It well explains that the sheet carrier density difference between InSb and InAs0.1Sb0.9 QWs mainly originates from this band diagram difference and the positio...

Quantum Hall Effect and Spin Resolved Anti‐crossing of Landau Levels in AlGaSbAs/InAs and AlInSb/InAsSb Quantum Wells

We have investigated transport properties in InAs/AlGaSbAs and InAsSb/AlInSb quantum wells (QW) in the quantum Hall regime. The carrier density in InAs QW is tuned by using a front gate bias, and the contour plot of resistance as a function of perpendicular magnetic field and gate voltage reveals the spin‐resolved subband‐Landau‐level coupling in tilted magnetic fields. An anomalous transport occurred by the coexistence of electrons and holes in the system has been observed both in InAs and InAsSb QWs.

SPIN RESOLVED SUBBAND-LANDAU-LEVEL COUPLING AND ELECTRON-HOLE COUPLING IN InAs/AlGaSbAs QUANTUM WELL

We have investigated the magneto-transport properties in InAs/AlGaSbAs quantum well (QW), where the lattice mismatch is less than 0.5%. In tilted magnetic fields, the spin-resolved subband-Landau-level coupling has been clearly observed in the magneto-resistance due to the large g-factor of this QW. An anomaly in the Hall effect has been observed at high magnetic fields of the filling factor being less than unity, which is caused by the coexistence of electrons and holes in the system.